Revert r211771. It was: "[X86] Improve the selection of SSE3/AVX addsub instructions".

This chang fully reverts r211771.
That revision added a canonicalization rule which has the potential to causes a
combine-cycle in the target-independent canonicalizing DAG combine.

The plan is to move the logic that forms target specific addsub nodes as part of
the lowering of shuffles.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213736 91177308-0d34-0410-b5e6-96231b3b80d8